It is known in the field of optical communications to use optical wavelengths as optical carriers for carrying digital or analog information. Also, the different wavelengths may be used to discriminate one set or channel of information from another. When a plurality of wavelengths are coupled or multiplexed onto a single fiber, this is called wavelength division multiplexing (WDM). Use of such WDM increases the overall bandwidth of the system.
There is a need in such systems to selectively switch various optical wavelength signals passing along one fiber to any of a number of other fibers. Such a switch is known as an optical router. A number of wavelength dependent switches and routers exist in the prior art. In U.S. Pat. Nos. 7,468,840, 7,558,447, 7,454,100 and U.S. Patent Application publication No. 2008/0316585, all hereby incorporated by reference, each in its entirety, there are disclosed various wavelength selective switches and routers, wherein an input optical signal undergoes spatial wavelength dispersion and polarization splitting in two different planes, which can conveniently be perpendicular planes. The wavelength dispersion may preferably be performed by a diffraction grating and the polarization-splitting by a polarized beam splitter. A polarization rotation device, such as a liquid crystal polarization modulator, pixelated along the wavelength dispersive direction such that each pixel operates on a separate wavelength channel, is operative to rotate the polarization of the light signal passing through each pixel, according to the control voltage applied to the pixel. The polarization modulated signals are then wavelength-recombined and polarization-recombined by means of similar or the same dispersion and polarization combining components as were used to respectively disperse and split the input signals. At the output polarization recombiner, the direction in which the resulting output signal is directed is determined by whether the polarization of the particular wavelength channel was rotated by the polarization modulator pixel, or not.
In US Patent Application publication No. 2008/0316585, there is described a multi-port switchable router, using beam steering elements which can be either an array of Micro-Electro-Mechanical System (MEMS) components, such as micro-mirrors, or a set of serially disposed liquid crystal arrays and wedge shaped birefringent crystals, which generate different angles of propagation to the beam passing therethrough according to the different polarizations of the beams produced by the setting of the liquid crystal array pixels, or a liquid crystal-on-silicon (LCOS) spatial light modulator acting as a phased array. Such routers can be conveniently constructed having 10 ports or more, and can be generally configured as a 1×9, or a 9×1 unit. In order to reduce the angular deviation required of the beam switching element, it is common to have the input port at the center of the port array, such that the element need only move one half the total port span, but in each direction.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.